"It was a very, very powerful event," says Margaret Campbell-Brown, an astronomer at the University of Western Ontario in London, Canada, who has studied data from two infrasound stations near the impact site. Her calculations show that the meteoroid was approximately 15 metres across when it entered the atmosphere, and put its mass at around 40 tonnes.

The infrasound stations are owned by Comprehensive Test Ban Treaty Organization, and are designed to provide independent data on weapons tests. The Russian meteor was substantially more powerful than the North Korean nuclear weapons test this month.

Brumfiel also reports that no scientist saw the meteor strike coming, which would have become visible a day or two ago. We might find out more about the meteor strike from military satellites, if the government decides to release that data.

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